I have gone through your query and understood the concern. Whenever there is a changeover of hormone medication, it is natural to experience menstrual disturbances. This is the most likely cause for the mid-cycle bleed you had experienced. Also, you should use additional protection similar to the initial cycle. In the current scenario, you can have a pelvic/trans-vaginal sonogram to know the status of the pelvic organs and also to confirm/exclude pregnancy
. If negative, please go ahead with the pill as things usually settle down in a month or two. Hope this helps.